Variable speed drive



May ll1, 1937. A. MAURER 2,080,145

VARIABLE SPEED DRIVE Filed Feb. 29, 1936 2 Sheets-Sheet /QVMQVM May 11, 1937. A* MAURER 2,080,145

VARIABLE SPEED DRIVE Filed Feb. 29, 1936 2 Sheets-Sheet 2 AParenteel May 11, 1931 PATENT. oFFicE 2,080,145 VARIABLE SPEISID DRIVE Albrecht Maurer, Bad Homburg vor der Hohe, f-

Germany, assignor to Link-Belt Company, Chlcago, Ill., a corporation of Illinois Aiipummn Febmmza. 19u. semi No. 66,345

( InGermany March l, 1935 i 17 Claims.

This invention relates to speed controls for lathes and other generally analogous cutting, shaplng,surfacing and linishing tools and machines. Y

It has for one object to provide automatic means for maintaining a constant cutting speed. another object is to provide in connection with devices* of the` general type indicated automatic means for maintaining constant cutting speed lo which is automatically varied in response to the changing or variable diameter of the piece which 1S being cut, surfaced, iinished or otherwisel worked upon. Another object is to provide such a control 'which may be readily combined or used 15 with a. main drive, embodying stepless or substantially stepless driving means. The problem is complicated'where the lathe or similar machine may be used at many different cutting speeds. Thus, if only one initial cutting speed is to be used, the problem of maintaining a constant cutting speed as the diameter ofthe work changes is relatively simple. .While, if the lathe may be used at a variety of initial cutting speeds, the problem o f providing an automatic 25 speed control, which will maintain a constant cutting speed, irrespective of' the original cutting speed for which the machine is set for a particular operation, or on a particular piece of work, is greatly complicated. It is, therefore, one of the objects of the present invention to provide not only an automatic means for maintaining a constant cutting speed, but to provide such a ,means suitable for eiective use with a machine which may be operated or may be set to operate for a wide variety of initial cutting speeds.

Other objects will appear from timeto time in the specification and claims. o

The invention is illustrated more or less diagrammatically in the acompanying drawings,

whereim- Figure l is a vertical section with parts in elevation and parts in section and Darts broken away, taken at line il--I of Figure 2;

Figure 2 is a plan view to which the lathe and the control have been applied;

lligure 3 is a diagrammatic View in perspective,

V withpartsin section and parts omitted, showing `j la, modiiied' form of the device; 50

'th ''moi'liflc'ation of vthe control;

` the intermediate control shaft 4.

Figure., 'lis a view somewhat similar to Figure 3,

` ng,diagrammatically. in perspective a furf ef5 isf-a'v diagram with parts in section rand (ci. 11a-21) Figure 6y is a plan view with parts omitted. illustrating a further modification. y

The invention as illustrated herewith is applied to a lathe, conventionally shown. It might, however, be applied to any sort oi mechanism which is used for turning, cutting, nishing or surfacing a piece of work. In general the lathe comprises means for holding and for rotating the work and for holding and moving a tool, the tool being arranged on a carriage which is moved toward the center of rotation as the cutting and surfacing progresses, the cutting or surfacing commencing upon the work at a given distance from the center of rotation and the tool being moved as the work' continues successively to points at a different distance from the center of rotation until the work is completed.

As shownin Figures 1 and 2, I is a lathe, 2 is a cross slide member arranged to carry a tool 2a in a suitable tool carrier. The slide moves in guides of any desired sort and is adjusted as to position by a hand wheel 3. Any suitable tail stock may be provided for supporting the work at one end. None is shown here as the details of the lathe in this respect form no essential part of the present invention. Likewise any suitable head stock may beprovided. The details of this are not described herewith because they form no essential part of the present invention. It is suilcient to say that the invention is applied to a lathe having means for holding the work and for rotating it.

Munted in suitable bearings along one side of; the lathe as an intermediate control member is a shaft 4 which is mounted in a generally horizontal position and in alignment with some part of the lathe, preferably the bed. Double levers 5 may be mounted upon a hub member 5a which is slidable longitudinally of the shaft I and is prevented from turning with respect to the shaft by being splined upon it or otherwise secured to it, for example, by a groove and a spline. A link 6 is pivoted between the double levers 5, at one end as at 1 and at' its opposite end is pivoted to the cross slide 2. Displacement of the cross slide in response `to movement of the adjusting wheel 3 acts through the link 6 and the levers i to turn The levers 5 and the link 6 are proportioned with respect to the cross slide l2, which is moved to vary the diameter of the work, so that the control shaft 4 is'given al turning movement corresponding to the logarithm of the cross slide movement or displacement. The. positions indicated numerically on Flgureel are those suitable 'for' a cutting It will be noticed that in Figure 1 the levers 5 and the link 5 are shown by dash lines only to simplify the showing of the parts and to ayoid obscuring other parts shown in the figure.

In order to vary the speed with which the work.

piece is driven, the intermediate control shaft 4 must be connected to the drive control. This is accomplished by the gear 8 which is mountedl on the shaft 4 andwhich meshes with a corresponding gear 8 which latter is fixed on the adjusting shaft I of a speed regulating device. In the form shown -in Figures 1 and 2 this speed regulating device is associated with an adjustable stepless drive so as to change the adjustment-of that drive and thereby to vary -the speed of rotation of parts driven from it. y a

'Ihe drive as illustrated diagrammatically inl Figure 1 maybe similar to that shown in my copending application Serial Number 628,158, filed August 10, 1932, and comprises two pairs of conical pulleys II, each pair arranged so that the pulleys can be moved toward and from each other, the pulleys' of one pair being moved toward each other as the pulleys of the other pair pulleys just described, an electric motor of variable speed or other variable speed control gear might be used'. In fact any such variable speed drive may be used provided the control of thisD is such that movement of the lregulating device or adjusting shaft I0 brings about a. logarithmic change of the driven R?. P. M.

Whatever the exact form of the drive, whether it be a steplessgear shown, or an electric motor or some other drive, the turning movements of the intermediate control shaft 4, which are 1 caused by movementsof the cross slide 2, cause a rotation of the adjusting shaft I0 and through this movement cause a variation in the speed of drive so that the cutting speed remains the same throughout, irrespective of change of the work diameter.l The shapes and proportions of the gears ,8 and 9 are such that the movements of the control shaft 4 bring about equal movements of the adjusting shaft I Ii'and consequently bring about equivalent movements of the stepless ad- .instable drive II.

In Figure 1, I Ib is the shaft which is driven by a motor or other suitable power source. This motor is not shown in the drawings. iIc is the secondjshaft of the vstepless drive which is driven by th b'elt or chain IIa and it acts to drive the belt or chain. IId. The belt IId works over an idler I Ie and a second idler I If to drive the pulley Iig on the cone pulley. The remainder of thev drive is typical of well known lathes and need not be described in detail. Suitable gearing is provided in the lathe drive proper for rotating the head stock or facfefplate, and consequently for rotating the work.

In order to adjust manuallythe basic or starting R. P. M., independent of the connection ofA aos/0h45 movement of the shaft 4 without slipping to the adjusting shaft I Il. The driven part I2' of the friction coupling I2 is coupled through the shaft Illa with a hand control lever I3 by means of which the gear can be adjusted, the hand lever I3 being effective to overcome the friction in" the friction coupling I2 so that when the hand control lever I3 is operated, the intermediate control shaft 4 remains at rest, being held in place by the connection through the levers 5 and the link 6 to the cross slide 2.

It is to b e understood that in place of the/friction coupling I2, I2', any other dlsengageable connection between the intermediate control shaft 4 and the adjusting spindle I0 of the gear.

nection with the manual control lever I3. Such a.'

device is illustratedin my co-pending application Serial No. 628,158.

Whitle the device of the present invention I might be designed for a considerable range of diameters to maintain the constant cutting speed required, the particular form shown herewith is designed for diameters from 5 0 to 400 mm. and will maintain accurately a constant cutting speed throughout this range. y

On Figure 2 the control lever I3 is in part broken away. but its several positions are, however, indicated on the figure. A number of positions of the control lever I3 are indicated and for each position there is shown on the drawing the diameter figures and the corresponding R. P. M. for a constant cutting speed of 31.4 metres per minute. Another cutting speed might be selected and the positions and rotations and diameters would be differentbut those indicated serve as a particular example.

The lever I3 is provided with a reading index I4 by means of which, in accordance with the invention set out, in my co-pending application 628,158, it is possible to read off any desired set of values of corresponding cutting 'speed and work diameter.

In the modified form of Figure3, instead of using the levers 5 and the link 6 to cause the desired rotation in the intermediate control shaft 4, a cam arrangement is'shown. The cross slide 2 has attached to it a cam member I5 which is provided with a suitably designed curved face as shown.' In contact withthe curved face, to 'run along it is a roller I6 carried by a lever I1. This lever is attached to the intermediate control shaft by being splined to it or being Aattached by a spline and groove or otherwise, so thatit may slide along the shaft but may not rotate withrespect to it. As shown, the weight of the roller I6 and the llever I'I is sufficient to hold the roller constantly in contact with the face of the cam. A counterweight might be added or spring means might be provided for accomplishing this,

but ordinarily the weight of the parts themselves is sufficient. The shape of the cam is' such that the movement of the cross slide 2. The movement of the shaft 4 is effective through the gears 8 and 9 upon the-shaft IIIvin the manner shown in and described in connection with the form of the device shown in Figures 1 and 2.

For some purposes it is ydesirable to provide an additional drive for the intermediate lcontrol shaft 4. In the forms of the'device thus far u "a control, but to provide an additional positive driving means for rotating the intermediate control shaft 4 in response to movement of the cross slide. An arrangement for accomplishing V this result is shown diagrammatically in Figure 4 in which a motor is provided for driving the shaft 4. Mounted upon the shaft 4 and keyed to itis a lever I8 which carries at one end a pin I9 positioned generally parallel to the shaft 4 and serving as a pivotal support for a second lever 29. This lever is provided at one end with a roller' 2|, which rests upon the face of the cam I5 which latter is attached to and moves with the cross slide 2. The lever 20 is so supported that it is overbalanced on the end which carries the roller 2| and thus the weight of the parts alone holds the roller in contactwith the' cam face. At its opposite end the lever 29 carries a generally U-shaped contact member 22 which preferablyfsurrounds the shaft 4.

lThe lever I8 carries two pairs of contacts 23, 24 and 25, 26,'the contacts being insulated from each other. The contacts are connected by suitable wiring with a source of current and through a relay 21 are connected with an electric motor 28. The wiring is such that when one pair of contacts is actuated the motor will be driven in one direction and when the opposite pair of f contacts is actuated it will be driven in the op- .posite direction. 'I'he motor carries a worm 29 f. the contact 22 into contactwith one pair of contacts, thus closing the gap either between the contacts of the pair 23, 24 or that between the pair 25, 26, and whichever pair of contacts is contacted and whichever circuit is closed, the electric motor 28 is placed in operation by the relay 21 and so the motor rotates in one direction or the other and moves the shaft 4 until the lever I8 again lies in a piane parallel to the lever 20 andthus again moves the contact 22 into the non-contact position, breaks the circuit and stops the'motor.

The rotation of the shaft 4 in the form shown in Figure 4 is transmitted through the gears 30, 3| to the device for controlling the speed of rotation. It is indicated diagrammatically as including the shaft I0 which has been shown and described in greater detail in connection with the form of the device shown in Figure 1.. It is to be-understood that the same drive for the lathe'shown in Figure 1 may be used in the form of the device shownin Figure 4. In this latter form of thedevice the control lever I3 for the independent manual adjustment is the same as l that shown and described earlier.

As shown in Figure 5 a still further means is provided for varying the position of the shaft 4 by means of a positive electric drive associated with a control which is actuated by movement attached to or associated with the crossslide.

There are arranged upon the contact bar certain contacts 33. "It will be noticed that in the form shown they are spaced from each other at varying distancesv and each corresponds to a fixed Work diameter ratio and the transition or movement from one contact to the next corresponds to a proportional change in the work diameter. Contacts 34 and 35 are provided on a swinging support 36. 'Ihe contacts are connected by suitable wiring to a relay 21 which is also in circuit with the severalcontacts 33. The contact carry. ing member 36 moves or swings in accordance with the direction of movement of the contact bar 32. As shown in Figure 5 it has been swung to the right in response to movement of the bar 32 to the right. In this position the contacts 33 of the bar come successively into contact with the contact member 34. Upon motion to thev left the member 36 is swung from the position shown and thus the contact 35 comes into operation, while the contact 34 is swung up out of operation and in movement to the left, therefore, the contact 35 co-operates with the contacts 33 successively throughout the continuwith one or another of the contacts 34 or 35, the

circuit for the electric motor 28 is closed through the relay 21 and the motor commences to run.

vThe motor is designed so that it automatically stops after a predetermined amount of movement, for example, after one or more revolutions. Obviously some automatic motor control may be associated with the motor to cause it automatically to stop after a predetermined amount of rotation. By means of the arrangement of Figure 5, a new contact 33 is brought into cooperation with one or another of the contacts 34 or 35 whenever the turning diameter of the work piece has changed to a degree sufficient to necessitate a change in the speed of rotation of the drive. The contacts may be so spaced` that they automatically eiect this re-adjustment whenever a change in diameter of, say 10%, has occurred. Obviously the contacts can be arranged .to act for a greater or a less proportional change in diameter.

The shaft 4 is rotated from the motor 28 in the form shown-in Figure 5 by means of gears 29 and 29a in the same manner as shown in Figure 4, and this transmission, including tho gears 29 and 29a, is so proportioned that upon each rotation or period of movement of the motor the shaft 4 is rotated to such an extent or through such a degree that the R. P. M. control device, including the shaft I0 and associated parts, is moved suiliciently to vary the R. P. M.' in accordance with the change in diameter which has occurred.

The form of the device shown in Figure 6 is generally similar to that shown in Figure 5 except that the contacts 33, instead of being ar ranged upon arack or bar, are mounted about a rotary number. As shown they are arranged in a helical line upon a drum or pulley 31. This pulley is rotated through gears '33 which engage a rack 39. 'Ihis rack as shown is attached to the cross slide 2. This arrangement of the contacts about a drum or pulley permits a very finely stepped subdivision of the entire diameter range without bringing the individual contacts 33 too close to each other for convenient or effective association with the contact 34 or 35 on the member 36.

The mechanism of the invention has been deall driven R. P. M. n or, in other words, for any scribed above in connection with the several desired cutting speed v. i

forms shown and the various parts and their In the drawings there have been shown by4 V' operation have been described. While the mech-` way of example a number of possible embodianism can be designed in accordance with a va ments of the invention and of the calculations riety of mathematical calculations, the calculaaboveset out. It is to be understood, of course, tions set out below indicate onesolution of the that there are many other `embodiments which problem. fall within theinvention and that the inven- In accordance with the present invention the tion is not limited in its practical application or problem of providing and maintaining actual embodiment merely to those shown in the at-A constant cutting sp'eed is solved in the following tached gures. manner: The radial displacements of the tool I claim: are converted into motions of an intermediate l. In combination with a lathe or the like, control member, the ratio-of which is equal to having a variable speed drive, means for malnthe logarithms of the radial displacements and taining automatically a constant cutting speed 15 the parts are so related and proportioned that irrespective of changes in the diameter of the through the motion of an intermediate control work, said means comprising atool holder, means member a control device is adjusted to influence for moving it radially with respect to the work, or control the R. P. M. Through the operations and control means associated with the drive of of this control device like movements of the adsaid lathetocontrol the speedthereof, and elecjusting device bring about changes in the R. P. trical means actuated by movement of said tool M., the ratio offvvhichl is equal to that of the holder to-aiect said control means, said electrical logarithms of the R. P. M. Thus it is possible means comprising a plurality of spaced contact I to develop an arrangement by meansl of which point members, a contact part adapted to conthe'lcontrol device which controls or influences tact one of said point members, and means for 25 the R. P. M. can be separated' from the intermoving said point members progressivelypast mediate control niember and can be adjusted said contact part, whereby movement of the tool 01 COIltIOlled independently t0 give any desired holder is eiective upon said control means to basic4 R. P. M. Y vary the speed of the drive to produce constant The device of the present invention embodies cutting speed. ,Y the following mathematical relations: 2. In combination with a lathe or the like, Between the work diameter 2r, the R. P. M. n having a variable speedA drive and manual means and the cutting speed v there exists the relation: for setting it, means for automatically maintaining a constant -cutting speed irrespective of 3"":9 changes in the diameter` of the work, said means or comprising a. tool holder, means for moving it v radially with respect to the work, and an auxm 2 1;F iliary control means associated with the drive of said lathe to control the speed thereof, and an For c-mtant cutting sped v z'c there results electric drive between said tool holder and said rnr-C control means whereby movement of the tool m m. m 'loganthms holder is effective upon said control means to a control device for the R. P.- M. is presupposed vary the speed of the drive to produce constant 10g "fi-10g n=10g C- cutting' speed.

In accordance with the invention the chan es 3' In ,ombmation with a lathe or the like' in KT are transmitted mm mtions y at the ism having a movable tool holder, a work holder and termediat control member m accordance with. means for driving the work holder to rotate they t e n z work, and a speed control for said driving means h fo owing *formula having manual setting means, an auxiliary auto- 11=c log r+log ci matic means associated with the tool holder for maintaining a constant cutting speed irrespective'of the diameter of the work, said means comprising an intermediate speed control including a plurality of cams and associated wh said tool holder to act in,response to moveme ts thereof to change Lthe R. P. M. of the work holder l n+log c2 drive.

Furthermore in accordance with the invention in connection with which the motions z ofthe adjusting device lead to changes of the R. P. M. n in accordance with theformula If. in accordance with the invenlmn the m0' having a movable tool holder, a work holder and tionsv 1l 0f the intermediate Centlol member are means for driving the work\ holder to rotate the used aS adjUSting mOtODS 2 fOI- 4the R- P- M- work, and a speed control for said driving means regulating device, and if therefore there is enhaving manual setting means, an auxiliary autotered y=zthere follows: matic means associated with the tool holder hfor clog r 10g c1= c1o n lo c2 maintaining a constant cutting lspeed irrespecg tive of the diameterof the work, said means .j comprising an intermediate speed control linked =l0g C to said tool holder, for relative movement with y respect thereto, the linkage being such thatythe Therefore, the desired relation exists between -ratio of movement of said intermediate control 1' and n. is equal to the logarithms of the radial displace- The change of the basic adjustment of the ments of said tool holder, the said intermediate log r-I-log nilog 012mg c yR. P. M. regulating .device corresponds'to the speed control being adapted to act in response change of c2. It is therefore possible by chang- .to movements thereof to change the R. P. M. of ing the basic adjustment to obtain any desired the work holder drive, the parts being so proporvalues of C and in this way adjust the device i'or tioned that the ratio of movements ci the ad- 4. In combination with a Alathe or the like,

a Cadeaus justing device to changes in the speed is equal to the logarithms of the R. P. M. of the work holding drive. 2

5. In combination with a lathe* or the like,

. 5 having a variable speed drive and manual means for setting it, means for automatically maintaining a constant cutting speed irrespective pf changes in the diameter of the work, said means comprising a tool holder, means for moving it radially with respect to the work, and an auxiliary control means associated with the` drive of said lathe to 'control the speedl thereof, and a connection between said tool holder and said control means whereby movement of the tool l5 holder is effective upon said control means to -vary the speed of the drive to produce constant cutting speed, and a friction connection between said manual means and said auxiliary control, whereby manual setting of the variable speed 20 drive may be accomplished irrespective of the position of the auxiliary control. V 6. In combination\with a lathe or the like, having a variable speed drive and manual means for setting it, means for automatically maintain- 25 ing a constant cutting speed irrespective of changes in'the diameter of thel work, saidA means comprising a tool holder, means for moving it radially with respect tothe work, and an auxiliary control means associated with the drive vof 30said lathe to control the speed thereof, and an electric drive between said tool holder and said control means whereby movement of the .tool holder is effective upon said control means to vary the speed of the drive to produce constant cutting 35 speed, and a friction connection between said manual means and said auxiliary control, whereby manual setting of the variable speed drive may be accomplished irrespective of the position of the auxiliary control. v

7. In combination with a lathe or the like, having a movable tool holder, a work holder and means for driving the work holder to rotate the work, and a speed control for said driving means havingmanual setting means, an auxiliary automatic means associated with the tool holder for maintaining a constant cutting speed irrespec'-,

tive of the diameter of the work, and a frictionconnection between said manual means and said auxiliary control, whereby manual setting of the 50 variable speed drive may be accomplished irrespective ofthe position of the auxiliary control.

a 8. In'combination with a lathe or `the like,

having a movable tool holder, a work holder and Ameans for driving thejwork holder to rotate the 55 work, and a speed control for said driving neans having manual setting means, an auxiliary automatic means associated with the tool holder for maintaining'a constant cutting speed irrespective of the diameter of thework, said auxiliary automatic means*` comprising an intermediate control shaft and parts associated' therewith and effective to convert radial movement of the tool holder into rotation of s'aid shaft.

9. In combination with a lathe or the like, having a movable tool holder,a work holder and means for driving the work holder to rotate. the

work, and a speed control for said driving means having manual setting means, an auxiliary automatic means associated with the tool holder for maintaining a constant cutting speed irrespective of the diameter of the work, said auxiliary automatic means comprisingA an intermediate control shaft and parts associated therewith and effective to convert radial movement of the tool comprising aicrank on said shaft and a link obnnecting said crank to said tool holder. l

10. In combination with a lathe or the like, v*having a movable tool holder, a work holder and means for driving the work holder to rotate the work, and a speed control for said driving means having manual setting means, an auxiliary automatic means associated with the tool holder for maintaining a constant cutting speed irrespective of the diameter of the work, `said auxiliary automatic means comprising an intermediate control shaft and parts associated therewith and effective to convert radial movement of the tool holder into rotation of said shaft, said parts `comprising a cam movable in response to movement of said tool holder, and a cam follower in contact with said cam and carried by a lever joined to said auxiliary shaft to permit relative sliding movement of the lever and shaft and to prevent relative turning movement of the two. 11. In combination with a` lathe or the like.

-having a movable tool holder, a work holder and means for driving the worknholder to rotate the work, and a speed control for said driving lmeans having manual setting means, an auxiliary automatic means associated with the tool holder for maintaining a constant cutting speed irrespective of the diameter of the work, said auxiliary automatic means comprising an intermediatev control 'shaft and parts associated therewith.. linked caried by a lever Joined to said,auxiliary shaft `to ermit relativesliding movement of the lever and lshaft and to prevent relative turning movement of the two, the path of the cam shaped to cause a turningmovement oi' the shaft in response to radial movement of the cam in a ratio equal tothe logarithms of the two movements.

` 12. In combination with a lathe or the like.

means for driving the work holder to rotate the work, and a speed control for said driving means having manual setting means, an auxiliary automatic means associated with the tool holder for maintaining a constant cutting speed irrespective `of the diameter of the work, said auxiliary means including an electric motor, an auxiliary shaft and electrical connections between said motor and said tool holder to cause movement of the tool holder to actuate the` motor to rotate the shaft in response to movement of thestool holder to a degree proportional to thatmovement.

13. In combination with a lathe or the like,

lhaving a movable tool holder, a work holder and having a movable tool holder, a work holder and means for driving the work holder to rotate the work, and a speed control for said driving means having manual setting means, ari-auxiliary automatic means associated with the tool holder for maintaining a constant cutting speed irrespective of the diameter of the work, said auxiliary means including an electric motor, an auxiliary shaft and electrical connections between said motor and said tool holder to cause movement of. the tool holder to actuate the motor to rotate the shaft in response to movement of the tool holder to a degree proportional to that movement, said electrical connection comprisingua contact device moved in responsev to movementl of lsaid tool holder, and wiring connections arranged to cause the motor to rotate in one direction or the other in. correspondence with th'e direction of movement of said tool4 holder.

5 14. In combination with a lathe or the like,

` having a movable tool holder, a work holder and means for driving the work holder to rotate the work, and a speed controlfor said driving means having manual setting means, an auxiliary automatic means associated with the tool holder for maintaining a ,constant cutting speed irrespective of the diameter of the work, said auxiliary means includingl an electric motor, an auxiliary shaft and electrical connections between said motor and said tool holder to cause movement of the tool holder to actuate the motor to rotate the shaft in response to movement of the tool holder to a degree proportional to that movement, said auxiliary shaft carrying ilxed upon it a contact arm, a second arm carried thereby and mounted to be rotated by movement of the tool hlde relative rotation of the said second arm with re-I spect to the said rst arm eiective to complete a contact to set the motor into operation.

15. In combination with a lathe or the like,

having a movable tool holder, a work holder and means for driving thework holder to rotate the Work, and a speed control for said driving means shaft in response tomovement of the tool holderto a degree proportional to that movement, said auxiliary shaft carrying iixed upon it a contact arm, a second arm carried thereby and mounted to be rotated by movement of the tool holder, relative rotation of the said second arm with respect to the said ilrst arm eiective to complete form cutting speed irrespective of changes in the diameter of the work, said devi characterized by the fact that radial displacements of the tool holder are converted into motions of said intery mediate control member, the ratio of which is equal to the logarithms of the radial displacements and characterized further by the fact that by the motions of the intermediate control member an R. P. M. controlling device is adjusted so that similar movements of the R. P. M. control device eect changes in the R. P. M. in accordance with a ratio which is equal to the logarithms of the R. P. M.

17. In combination with a lathe or the like, having a movable tool holder, a work holder and means for driving the work holder tov rotate the work, and a speed control for said driving means having manual settingmeans, an auxiliary automatic means associated with the tool holder and comprising a plurality of cams for maintaining a constant cutting speed irrespective of the diameter of the work.

ALBRECHT MAURER. 

